This invention relates to gauge technology, and in particular to magnetically driven gauges having a magnetic sensor and detector to provide signal output.
Liquid level gauges are frequently employed to monitor the level in a LP gas tank. There are instances where it is desirable to have both a visual indication of fluid level and an electrical indication of the fluid level. In the area of LP gas measurement, a magnetic drive feature is important because the fluid is stored under pressure. A magnetic drive allows a signal from the float mechanism inside the tank to be transmitted through a solid, non-magnetic bulkhead without the necessity of dynamic seals or pressure-type conductors. Many magnetic liquid level gauges suitable for LP gas which include a magnetically-driven dial assembly are known such as that disclosed in U.S. Pat. No. 4,987,400 assigned to Rochester Gauges of Dallas, Tex. Also, there are many designs known for the construction of float arms and drive assemblies for use with liquid level gauges. These are exemplified in patents, such as U.S. Pat. No. 6,089,086.
In the past, liquid level gauges for LP gas provided a visual reading or a visual reading and an electronic output. Previous designs of liquid level gauges for magnetically driven gauges which produce an electrical output signal had the disadvantages inherent in using variable resistors with a wiper arm contact. The designs were subject to mechanical wear and a relatively complex construction involving a number of parts. Thus, there has been a need for a more reliable and simplified design for these LP liquid level gauges which provide an electrical output related to the liquid level in the vessel.
Hall effect sensors have been employed in various automotive applications such as described in U.S. Pat. Nos. 5,982,170 and 5,570,118 for controlling throttles. The magnetic connection of the Hall effect sensor is thought to be more reliable than systems which depend on the sliding contact of variable resistor devices.
LP gas is stored in pressurized containers which typically must meet certain governmental standards. The industry has current standards for the gauge head which mounts to the pressurized vessel. As a result, there are a great number of existing LP gas containers already equipped with existing gauges. The present invention has the advantage that the dial assembly of the present invention can be designed to be a retrofit on existing LP gauges with no need to change the mechanism of the float assembly within the tank. Many existing home and small business storage tanks are equipped with weak drive magnets suited for low friction direct-indicating dial assemblies. The present invention is low friction as there is no sliding wiper contact, and thus is compatible .with existing gauges equipped with weak drive magnets within the tank, also known as tank magnets. Another advantage of the present invention related to the strength of the drive magnet is that the pointer magnet acts as a magnetic shield between the gauge drive magnet and the Hall effect sensor, protecting the Hall effect sensor from stray magnetic interference. Thus, this makes the present invention compatible with gauges equipped with strong drive magnets. Also, many of these existing storage tanks do not include a dial assembly which provides for electrical signal output. For example, many existing home and small business storage tanks do not include a dial assembly which provides for electrical signal output. The present invention is advantageous in that it can be used as a retrofit on these vessels to provide an electrical output which can be utilized for remote monitoring of tank levels. With remote monitoring of tank levels, distributors of LP gas will be able to more efficiently plan deliveries to various consumers. For example, the ability to transmit an electrical signal of the tank level for various customers to a distributor of the LP gas, allows the distributor to plan the most efficient use of delivery vehicles. Currently, many distributors are responding to calls from customers who request a delivery, but who are not able to provide accurate information as to the quantity needed. Distributors also currently are using preplanned routes which are not based on actual need but projected need. As a result of weather fluctuations, these preplanned trips are often inefficient. The delivery truck either returns with a partial load or a second trip is required. The present invention facilitates remote monitoring of liquid level in storage tanks allowing for more efficient distribution of LP gas and other benefits.
The present invention also has the advantage of a design which minimizes the possibility of a mechanical failure due to wear since the magnet sensor, preferably a Hall device, is activated by changes in magnetic flux only, without the need of sliding contact of previous designs.
In one aspect, the present invention provides a magnetically driven dial assembly including a magnetic flux detector, preferably a Hall effect sensor. In one embodiment, the dial assembly includes a base which has a pivot axis, and preferably defines a cavity for receiving a shaped magnet. Extending from either the base or a cover, at the pivot axis, is a pin around which the shaped magnet rotates. Preferably, the shaped magnet has a generally circular shape in a plane substantially perpendicular to the axis of rotation, and has a variable thickness in a direction perpendicular to the plane (or parallel to the axis of rotation). Lying within the plane of the magnet is a magnetic axis upon which the north and south poles of the magnet are located on opposite sides of the center of the magnet. Preferably, the magnet includes a pointer, and the base is provided within indicia to indicate various liquid levels. A cap, or cover, is provided to encase the dial components, and a detector, including a Hall effect sensor, is removeablly positioned operatively adjacent to the shaped magnet. In a preferred embodiment, the cap defines a channel on its outside surface to receive a detector containing a Hall effect sensor.
In the preferred embodiment, a pointer is provided at the twelve o""clock position of the generally circular shaped magnet, and the north and south poles are located at the three o""clock and nine o""clock positions of the shaped magnet. The thickness of the magnet is greatest at approximately the eleven o""clock and one o""clock positions with the thickness decreasing from both positions to the thinnest part of the magnet at the six o""clock position. The distance between the Hall effect sensor and shaped magnet varies as the shape magnet rotates because of the variable thickness of the shaped magnet.
In another aspect, the present invention relates to a magnetically driven gauge which includes a gauge head, a movable float, and a float magnet which rotates in response to changes in the float position together with a dial assembly as described above.